Copper-base alloys having resistance to dezincification

ABSTRACT

Copper-base alloys are provided that maintain high hot forgeability and cuttability and low-cost feature and which still are improved in resistance to dezincification. The alloys comprise 57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based on weight, with a Si/Sn value in the range of 0.05-1, and the balance being Zn and incidental impurities.

BACKGROUND OF THE INVENTION

[0001] This invention relates to copper-base alloys having highresistance to dezincification corrosion which would otherwise occurduring use in corrosive aqueous solutions. The alloys also have good hotworking and cutting properties.

[0002] Cu—Zn alloys, commonly called brasses, have good workingproperties, both cold and hot, so they have found extensive use from oldtimes. Among the best known are forging brass bars (JIS C 3771),free-cutting brass bars (JIS C 3604) and high-strength brass bars (JIS C6782). These copper-base alloys share the common feature of including acontinuous β phase for better workability.

[0003] Zinc in the β phase has high ionization tendency, so in naturalenvironment, particularly in the presence of a corrosive aqueoussolution, it is selectively leached from the above-mentioned alloys.This is why those alloys are very poor in resistance to dezincification.

[0004] Various proposals have recently been made with a view toimproving the resistance to dezincification of brasses that aretypically used in parts that are brought into contact with water.According to Unexamined Japanese Patent Application (JPA) No.183275/1998, Sn is added to Cu—Zn alloys and, after hot extruding,various heat treatments are performed to control the proportion of the γphase and the Sn level in the γ phase, thereby improving resistance todezincification.

[0005] According to Unexamined Published Japanese Patent Application(JPA) No. 108184/1994, Sn is added to Cu—Zn alloys and, after hotextruding, the alloys are subjected to a heat treatment so that they aresolely composed of the α phase, thereby enhancing their resistance todezincification.

[0006] The new alloys described above are characterized by having Snadded in larger amounts than the conventional brasses. However, the highinclusion of Sn in brasses has its own problems.

[0007] First, with the increase in the Sn level, the localsolidification time of brasses increases and there occurs inversesegregation of Sn during casting, producing ingots with surface defects.At the same time, the adaptability to extrusion and other hot workingprocesses is impaired, causing a significant drop in the yield of shapedproducts.

[0008] Secondly, in order to elicit the ability of Sn to improveresistance to dezincification, hot extruding must be followed by a heattreatment for generating a certain area of γ phase at grain boundariesof the α phase and causing Sn to diffuse uniformly in the γ phase.However, this adds to the overall production cost.

[0009] What is specifically taught in JPA No. 183275/1998 is as follows:a heat treatment is applied at between 500° C. (inclusive) and 550° C.(inclusive) for at least 30 seconds, then cooling to 350° C. is done ata rate no faster than 0.4° C./sec; alternatively, a heat treatment isapplied at between 400° C. (inclusive) and 500° C. (inclusive) for atleast 30 seconds, then cooling is done; or a heat treatment is appliedat between 500° C. (inclusive) and 550° C. (inclusive) for at least 30seconds, then cooling to 350° C. is done at a rate between 0.4° C./sec(inclusive) and 4° C./sec (inclusive). The teaching of JPA No.108184/1994 comprises hot extruding or drawing the alloy, followed by aheat treatment at 500-600° C. for a period of 30 minutes to 3 hours.

[0010] These heat treatments involve various problems. For one thing, inorder to ensure the appropriate conditions, costly equipment must beused. Secondly, depending on product size, the difference in heatpattern between the interior and exterior of the product can causevariations in microstructure, which makes the process lesscost-effective due to lower yield. Thirdly, products of complex shapeoccasionally suffer from the problems of dimensional changes, residualstress and so forth.

[0011] A recent proposal worth particular mention is free-cutting copperalloys having Si added to Cu—Zn alloys (JPA Nos. 119774/2000 and119775/2000). These alloys contain at least 1.8 wt % of Si with a largeportion of Cu/Si γ phase at grain boundaries of the α phase. Underenvironment of actual use, the Cu/Si γ phase has better resistance todezincification than the β phase but is not as resistant as a Cu/Sn γphase. If the Si content is 1.8% or more, the thermal conductivity ofthe material drops considerably and the blade of a cutting tool becomesunduly hot during cutting to cause many problems such as a shorter lifeof the cutting tool, lower precision in cutting and limit on the cuttingspeed.

SUMMARY OF THE INVENTION

[0012] The present invention has been accomplished under thesecircumstances and has as an object providing copper-base alloys thathave outstanding resistance to dezincification, hot forgeability andcuttability and which still can be fabricated at reasonably low cost.

[0013] The present inventors conducted intensive studies in order toensure that the addition of Sn would prove effective in preventingdezincification of copper-base alloys to the fullest extent and foundthe following: when Si as well as Sn were added and the ratio of Si toSn was adjusted to lie in an appropriate range, secondary dendrite armsgrew sufficiently thinner and longer during solidification to suppresssegregation of Sn; upon hot working, the γ phase was dispersed uniformlybetween regions of α phase. This phenomenon made a great contribution toimprovements in resistance to dezincification and hot workingproperties.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The stated object can be attained by any one of the followingcopper-base alloys having improved resistance to dezincification.

[0015] (1) A dezincification resistant copper-base alloy comprising57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based onweight, with a Si/Sn value in the range of 0.05-1, and the balance beingZn and incidental impurities.

[0016] (2) A dezincification resistant copper-base alloy comprising57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, allpercentages based on weight, with a Si/Sn value in the range of 0.05-1,and the balance being Zn and incidental impurities.

[0017] (3) A dezincification resistant copper-base alloy comprising57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with aSi/Sn value in the range of 0.05-1, further containing in a total amountof 0.02-0.2% at least one element selected from the group consisting of0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, all percentagesbased on weight, and the balance being Zn and incidental impurities.

[0018] (4) A dezincification resistant copper-base alloy comprising57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with aSi/Sn value in the range of 0.05-1, further containing in a total amountof 0.01-3% of at least one element selected from the group consisting of0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% ofCr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2%of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te,0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% ofCa, all percentages based on weight, and the balance being Zn andincidental impurities.

[0019] (5) A dezincification resistant copper-base alloy comprising57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with aSi/Sn value in the range of 0.05-1, further containing in a total amountof 0.02-0.2% at least one element selected from the group consisting of0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, still furthercontaining in a total amount of 0.01-3% of at least one element selectedfrom the group consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% ofMn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2%of Zr, 0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg,0.01-2% of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% ofLa, 0.01-2% of Cd and 0.01-1% of Ca, all percentages based on weight,and the balance being Zn and incidental impurities.

[0020] On the following pages, the criticality of the compositionalranges for the ingredients in the copper-base alloy of the invention isdescribed in detail.

[0021] Cu:

[0022] An increase in the Cu content adds to the α phase and improvescorrosion resistance but if its content exceeds 69%, there occurs amarked drop in hot forgeability. Since Cu is more expensive than Zn, theCu content is desirably minimized from an economical viewpoint. If theCu content is smaller than 57%, the proportion of the β phase increasesto improve forgeability at elevated temperature; on the other hand,resistance to dezincification decreases and so do the strength andelongation of the material. Considering these merits and demerits, thecompositional range of Cu is specified to lie between 57 and 69%,preferably between 59 and 63%, on a weight basis.

[0023] Sn:

[0024] Adding at least 0.3% of Sn is effective in improving resistanceto dezincification. What is more, the improvement in resistance todezincification is marked if the addition of Sn is increased. However,adding Sn in excess of 3% not only induces deep defects in the surfaceof ingots being cast but also fails to bring out a correspondingimprovement in the resistance to dezincification. In addition, Sn ismore expensive than Zn and Cu, so it is a factor in increasing theproduction cost. For these reasons, the content of Sn in the copper-basealloy of the invention is specified to lie between 0.3 and 3%,preferably between 0.5 and 2%.

[0025] Si:

[0026] Silicon is added for the particular purpose of improvingcastability and eliciting the ability of Sn to improve resistance todezincification. Adding a suitable amount of Si is effective inimproving the fluidity of a melt during casting and suppressing thesegregation of Sn. As a result, in the absence of any heat treatmentafter hot extruding and forging, the ability of Sn to improve resistanceto dezincification is elicited to the fullest extent, thereby providingconsistent and outstanding dezincification resistance and mechanicalcharacteristics.

[0027] If the Si content exceeds 1.5%, an increased amount of Si/Cu γ, κor β phase appears at grain boundaries of the α phase to deteriorate theresistance to dezincification. In addition, the increased amount of Sioxide is detrimental to castability and hot workability. If the Sicontent further increases to 1.8% or more, the thermal conductivity ofthe material drops considerably and the blade of a cutting tool becomesunduly hot during cutting to cause many problems such as a shorter lifeof the cutting tool, lower precision in cutting and limit on the cuttingspeed.

[0028] If the Si content is less than 0.02%, there is obtained no effectof improving castability or suppressing the segregation of Sn. For thesereasons, the compositional range of Si is specified to lie between 0.02and 1.5%, preferably between 0.06 and 0.6%.

[0029] Si/Sn:

[0030] The Si/Sn value is specified in the present invention since inorder to maximize the ability of Sn to improve resistance todezincification, Si must be added in an optimum amount that depends onthe amount of Sn addition. If the Si/Sn value is controlled at anappropriate level, secondary dendrite arms grow in a sufficiently finerand longer form during solidification to suppress the segregation of Snand, after hot working, the γ phase is dispersed uniformly betweenregions of α phase to improve resistance to dezincification whileassuring hot deformability. If the Si/Sn value is greater than 1, the Sicontent is excessive. Due to the high zinc equivalent of Si, thereoccurs increased precipitation of the β phase and the β phasesurrounding the α phase cannot be fragmented by the γ phase, whichresults in impaired resistance to dezincification. If the Si/Sn value issmaller than 0.05, the intended effect of suppressing the segregation ofSn is not attained and in order to elicit the effect of improvingresistance to dezincification, a heat treatment must be performed afterhot working. Therefore, the Si/Sn value is preferably in the range of0.05-1, more preferably in the range of 0.1-0.5.

[0031] P, Sb, As:

[0032] These elements are effective in suppressing dezincificationwithout impairing cuttability and forgeability. If their addition isless than 0.02%, the intended effect of suppressing dezincification isnot obtained. If their addition exceeds 0.2%, boundary segregationoccurs to reduce ductility while increasing stress corrosion crackingsensitivity. Hence, the contents of P, Sb and As are each specified tolie between 0.02 and 0.2%.

[0033] Pb:

[0034] Lead is added to improve the cuttability of the material. If itsaddition is less than 0.5%, the desired cuttability is not attained. Ifthe Pb addition exceeds 3%, hot working such as extruding or forging isdifficult to perform. If Pb is to be added, its compositional range isbetween 0.5 and 3%, preferably between 1.5 and 2.3%.

[0035] If desired, the copper-base alloy of the invention may furthercontain at least one element selected from the group consisting of0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% ofCr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2%of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te,0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% ofCa; these elements may be contained in a total amount of 0.01-3%. Ifadded in amounts within the specified ranges, these elements areeffective in improving mechanical characteristics and cuttabilitywithout damaging resistance to dezincification and hot workability.

[0036] The copper-base alloy of the invention with its compositionadjusted to the ranges set forth above has outstanding resistance todezincification, hot forgeability and cuttability and still can befabricated at reasonably low cost.

[0037] The mode for carrying out the present invention is describedbelow with reference to examples.

EXAMPLES

[0038] Samples of the dezincification resistant copper-base alloy of theinvention were prepared as described below. Comparative samples werealso prepared. The chemical ingredients listed in Table 1 were melted inan induction furnace and cast semicontinuously into billets (80 mm^(φ))at temperatures of the liquidus plus about 100° C. The castability ofeach composition was evaluated by checking the depth of surface defectssuch as inclusions in the cast billets. The results are shown in Table 1as evaluated by the following criteria: ⊚ (depth of surface defect<1mm); ∘ (1-3 mm); × (>3 mm). TABLE 1 Sample Chemical ingredients (wt %)No. Cu Zn Sn Si Si/Sn Pb P Fe Ni Invention 1 61.3 bal. 1.50 0.71 0.4731.7 — — — 2 59.5 bal. 1.38 0.65 0.471 1.8 — — — 3 60.2 bal. 1.40 0.630.450 1.9 0.07 — — 4 58.5 bal. 2.50 0.24 0.096 2.0 — — — 5 60.7 bal.1.08 0.20 0.185 2.0 0.04 0.11 — 6 61.2 bal. 0.87 0.21 0.241 1.9 0.050.13 0.17 7 61.8 bal. 1.00 0.12 0.120 1.7 0.05 0.10 0.30 8 61.2 bal.1.50 0.18 0.120 1.6 0.07 0.17 — 9 59.0 bal. 1.50 0.36 0.240 1.4 0.080.23 0.60 10 62.2 bal. 1.24 0.70 0.565 1.8 0.06 0.12 0.06 11 62.0 bal.1.24 0.60 0.484 0.8 — — — 12 61.8 bal. 1.16 0.30 0.259 1.5 — — — 13 60.8bal. 0.80 0.20 0.250 1.8 0.05 0.10 0.06 14 63.0 bal. 1.80 0.80 0.444 1.50.05 — — Comparison 15 62.0 bal. 1.50 — — 1.9 — — — 16 60.6 bal. 0.461.00 2.174 2.0 0.05 — — 17 59.0 bal. 0.20 0.01 0.050 — 0.04 — — 18 58.0bal. — 2.5 — 1.9 — — — 19 61.0 bal. — 3 — — — — — 20 59.0 bal. 1.5 1.91.267 — — — —

[0039] The 80-mm^(φ) billets were held at 800° C. for 30 minutes andlater hot extruded into bars having a diameter of 30 mm.

[0040] The as-extruded bars were evaluated for resistance todezincification, resistance to hot deformation, hardness, tensilestrength and elongation. The dezincification test was conducted by twomethods under different conditions, one specified in JBMA T303-1988 andthe other in ISO 6509-1981. Test samples as cut from the extruded barswere set so that the direction of corrosion coincided with the extrudingdirection. In order to investigate the extent of the change inresistance to dezincification that was caused by heat treatment,evaluation was also made for the resistance to dezincification ofsamples that were subjected to a heat treatment at 400° C. for 3 hours.

[0041] To measure the resistance to hot deformation, cylindrical samples15 mm in both diameter and height were cut on a lathe from the extrudedbars and subjected to a drop-hammer test. The test temperature and thedistortion rate were 750° C. and 180 S⁻¹, respectively.

[0042] The cutting test was performed by cutting on a lathe and chipfragmentation was evaluated by the following criteria: ∘ (all chips werecompletely fragmented); × (chips were not fragmented). For stickingproperty, 10 cutting tests were conducted with a continuous feed of 100mm and the results were evaluated by the following criteria: × (copperstuck to the tip of the blade); ∘ (no copper stuck). The cuttingconditions were as follows: rotating speed, 950 rpm; depth of cut, 0.5mm; feed speed, 0.06 mm/rev.; feed, 100 mm; cutting oil, none; cuttingtool material, superhard steel. The hardness of the copper-base alloywas Vickers hardness and measured according to JIS Z 2244 under atesting force of 49 N on a section perpendicular to the extrudingdirection. The tensile test was conducted in accordance with JIS Z 2241on No. 4 specimens which were stretched in a direction parallel to theextruding direction. The results of the tests are shown in Table 2.Maximum depth of Maximum depth of Resistance Cuttability Tensiledezincification by JBMA dezincification Sample to hot sticking to ChipHardness strength Elongation after heat by ISO (μm) No. Castabilitydeformation the blade tip fragmentation Hv MPa % as-extruded treatmentas-extruded Invention 1 ⊚ 78 ∘ ∘ 130 451 27 59 59 115 2 ⊚ 67 ∘ ∘ 132 44528 65 64 130 3 ⊚ 67 ∘ ∘ 129 433 34 60 60 125 4 ∘ 72 ∘ ∘ 141 452 25 41 3980 5 ⊚ 75 ∘ ∘ 107 407 45 57 55 115 6 ⊚ 76 ∘ ∘ 105 399 46 59 58 115 7 ⊚74 ∘ ∘ 110 445 45 57 56 110 8 ⊚ 73 ∘ ∘ 118 418 44 53 51 95 9 ⊚ 68 ∘ ∘133 467 44 52 52 95 10 ⊚ 68 ∘ ∘ 137 475 25 45 42 75 11 ⊚ 69 ∘ ∘ 135 43728 52 50 85 12 ⊚ 71 ∘ ∘ 124 415 33 55 53 95 13 ⊚ 77 ∘ ∘ 102 398 40 58 58105 14 ⊚ 73 ∘ ∘ 121 416 32 21 19 65 Comparison 15 X 79 ∘ ∘ 119 412 36 9271 135 16 ⊚ 67 ∘ ∘ 132 423 25 115 116 450 17 ⊚ 85 ∘ X  98 387 48 173 167835 18 X 75 X ∘ 140 440 21 134 135 745 19 X 73 X X 146 453 19 165 171585 20 X 65 X X 165 527 26 155 157 95

[0043] Sample Nos. 1-14 prepared in accordance with the alloycomposition of the invention showed outstanding castability, mechanicalcharacteristics and cuttability, as well as low resistance to hotdeformation comparable to that of hot forging alloy C 3771 (deformationresistance, 70 MPa). They all had high resistance to dezincificationsince the maximum depth of dezincification was no more than 65 μm inJBMA T303-1988 and no more than 130 μm in ISO 6509-1981.

[0044] What was particularly interesting about the samples of theinvention was that the maximum depth of dezincification as measured byJBMA was little different between the as-extruded state and theheat-treated state. It was therefore clear that by adding suitableamounts of Si, the copper-base alloys were given consistent andoutstanding resistance to dezincification even when they were justsubjected to hot working without any subsequent special heat treatments.

[0045] Sample Nos. 15-20 were comparisons and had various defects.Sample No. 15 did not contain Si, so it was not only low in castabilityand resistance to dezincification but also characterized by considerabledifference in the maximum depth of dezincification between theas-extruded state and the heat-treated state. Sample No. 16 had a Si/Snvalue beyond the range specified by the invention, so an excessive βphase surrounded the α phase, deteriorating the resistance todezincification.

[0046] Sample No. 17 contained less Sn and Si than the lower limitsspecified by the invention, so the proportions of the γ and κ phaseswere insufficient to prevent marked drop in resistance todezincification; what is more, the resistance to hot deformation wasgreat and chips could not be fragmented. Sample Nos. 18 and 19 did notcontain Sn, so they were poor in resistance to dezincification; inaddition, they contained more Si than specified by the invention, socopper stuck to the tip of the cutting blade showing how poor thecuttability of the material was.

[0047] Sample No. 20 contained both Sn and Si but the Si/Sn valueexceeded the range specified by the invention; what is more, the Sicontent was greater than 1.8%. Hence, the sample was poor in resistanceto dezincification and castability and copper stuck to the tip of thecutting blade.

[0048] As described above, the present invention offers copper-basealloys that have outstanding resistance to dezincification, hotforgeability and cuttability and which still can be fabricated atreasonably low cost.

What is claimed is:
 1. A dezincification resistant copper-base alloycomprising 57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, allpercentages based on weight, with a Si/Sn value in the range of 0.05-1,and the balance being Zn and incidental impurities.
 2. A dezincificationresistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn,0.02-1.5% of Si and 0.5-3% of Pb, all percentages based on weight, witha Si/Sn value in the range of 0.05-1, and the balance being Zn andincidental impurities.
 3. A dezincification resistant copper-base alloycomprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb,with a Si/Sn value in the range of 0.05-1, further containing in a totalamount of 0.02-0.2% at least one element selected from the groupconsisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, allpercentages based on weight, and the balance being Zn and incidentalimpurities.
 4. A dezincification resistant copper-base alloy comprising57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with aSi/Sn value in the range of 0.05-1, further containing in a total amountof 0.01-3% of at least one element selected from the group consisting of0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% ofCr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2%of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te,0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% ofCa, all percentages based on weight, and the balance being Zn andincidental impurities.
 5. A dezincification resistant copper-base alloycomprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb,with a Si/Sn value in the range of 0.05-1, further containing in a totalamount of 0.02-0.2% at least one element selected from the groupconsisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, stillfurther containing in a total amount of 0.01-3% of at least one elementselected from the group consisting of 0.01-2% of Fe, 0.01-2% of Ni,0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% ofBe, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2%of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y,0.01-2% of La, 0.01-2% of Cd and 0.01-1% of Ca, all percentages based onweight, and the balance being Zn and incidental impurities.